remove some jansson versioning info
remove some jansson versioning info

Summary:
Watchman jansson looks nothing like upstream jansson at this point, so
remove any semblance of versioning information.

Reviewed By: fanzeyi

Differential Revision: D35388353

fbshipit-source-id: 07166ff61e8abf21ac8b371d26d6a38e56dfa3cf

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman